Distillation process



Aug. 25, 1959 R. J. 'VENIS 2,901 ,405

DISTILLATION PROCESS Filed March '7, 1957 16V CYCLOPENTADIENE XYLENE XYLENE CYCLOPENTADIENE'FREE SIDE STREAM 2| BOTTOMS INVENTOR: REGINALD J. VENIS HIS ATTORNEY Patented Aug". 25, 1959 DISTILLATION PROCESS Reginald Jeremiah Venis, Manchester, England, assignor to Shell Development Company, New York, N.Y., a corporation of Delaware Application March 7, 1957, Serial No. 644,598

Claims priority, application Great Britain March 16, 1956 3 Claims. (Cl. 20240) This invention relates to the treatment of hydrocarbon mixtures containing primarily cyclopentadiene and higher boiling hydrocarbons, for example a mixture of alkyl benzenes, indene, cyclopen-tadiene, methyl styrenes and other alkyl derivatives of styrene and alkyl derivatives of cyclopentadiene. Such a mixture is obtained from the socalled cracked aromatic distillate obtained by thermally cracking a petroleum fraction of a boiling point range of 50-170 C., after benzene, toluene, xylene and lower boiling hydrocarbons have been removed.

It is an object of this invention to recover cyclopentadiene from cracked aromatic oils. It is another object to recover from cracked aromatic oils, in a form free from cyclopentadiene audits polymers, resin-forming unsaturated compounds boiling between 150 and 200 C., specifically, methyl styrenes and indene. Further objects and advantages of this invention will appear from the accompanying description thereof, which is made with reference to the sole figure of the drawing which illustrates in schematic form a method of carrying out the process of this invention.

In cracked aromatic distillates of the type described, some of the most valuable constituents are indene and methyl styreen, and accordingly it has been the practice to separate these compounds in a distillation step which involves passing the vaporized mixture at about 300 C. to the lower section of a fractionating column, provided with reflux, and removing the methyl styrene, alkyl benzenes and indene as a side stream having a boiling range of 150 to 190 C.

With a conventional reflux, however, the cyclopentadiene enters the column as monomer, passes out of the column with the overhead product, is condensed, collected in a receiver and is then to a large extent returned with the reflux. When the reflux heats up in passnig down the column, much of the monomeric cyclopentadiene is transformed into the dimer which boils at about 170 C. and will therefore not vaporize overhead, but leaves the column in the side stream. This involves an objectionable degree of contamination of the side stream since the dimeric cyclopentadiene has an adverse effect on resins produced from the indene and methyl styrene components of the stream. Moreover, the cyclopentadiene, itself a valuable starting material, for example for the production of insecticides, is lost.

These disadvantages are largely obviated and cyclopentadiene recovered by means of the present invention, according to which there is provided a process for treating a mixture comprising monomeric cyclopentadiene and resin-fonning compounds, e.g. alkyl styrenes and indene, which comprises feeding this mixture in the vapor state at a temperature which ensures that the cyclopentadiene is present in the monomeric form to or near the base of a fractionating column, at or near the top of which column is fed a relatively cold reflux stream of inert aromatic hydrocarbon, withdrawing as overhead product cyclopentadiene and inert aromatic hydrocarbon, the overhead temperature being maintained at a temperature between the boiling point of monomeric cyclopentadiene and the inert aromatic hydrocarbon, withdrawing a side stream of said inert aromatic hydrocarbon, cooling it and returning it as said reflux stream and withdrawing from the column at least a portion of the charge comprising said resin-forming compounds as a side stream boiling between 150 and 200 C., and preferably between 150 and 190 C.

The inert aromatic hydrocarbon is, in one method of operation, a mixture of xylenes obtained from the same cracking operation as that which provides the cyclopentadiene-containing mixture. These xylenes may be present in the feed to the fractionation column either by reason of specific addition, or by suitable control of the preceding distillation stage of the cracked petroleum products. The inert aromatic hydrocarbon, used as liquid reflux, is withdrawn from a lower plate of the fractionation column. This withdrawal must be made at an intermediate point (e.g. plate or tray 10 or 12 from the top), where no monomeric cyclopentadiene can be present in solution in the down-coming liquid and no monomeric cyclopentadiene in the up-going vapors can have been converted to the dimeric form.

More specifically, according to the present invention, a hydrocarbon mixture comprising predominantly monomeric cyclopentadiene, alkyl styrenes, indene and higher boiling compounds together with some xylene is introduced in the vapor state at a temperaturebetween 290 and 320 C. to or near the base of a column, liquid reflux is withdrawn at a temperature of about 150 C. from an intermediate point of the column where the liquid composition and temperature is such that substantially no monomeric cyclopentadiene can be present in solution and where there has been no formation of any substantial amount of dimeric cyclopentadiene, the reflux is cooled to about 40 C. and returned to or near the top plate of the column, the head ofthe column is maintained at a temperature of about 60 to 90 C., monomeric cyclopentadiene and xylene are removed as overhead products, and a cyclopentadiene-free side stream boiling between 150 and 190 C., comprising alkyl styrenes and indene, is withdrawn from the column.

The cyclopentadiene can easily be separated from the overhead product by a simple stripping operation, or the overhead vapor can be passed continuously to a subsequent column for fractionation and the monomeric cyclopentadiene recovered as an overhead product from this last column.

The process of this invention is particularly adapted to the treatment of cracked oils containing a relatively low concentration of cyclopentadiene, e.g. between 1 and 10 percent by weight and generally less than 5 percent, a relatively low concentration of inert aromatics such as xylenes, e.g. less than 10 percent by weight and generally less than 5 percent, a substantial concentration of resinforming compounds boiling between and 200 C., e.g. between 15 and 50 percent by weight, and higher boiling material, generally of a cyclic nature. The higher boiling fraction may contain further resin-forming materials. The cracked oil to be treated preferably contains little or no unsaturated compounds boiling below 150 C., except said cyclopentadiene. A small amount of styrene, however, has been found not to interfere in the desired separation.

Turning now to the drawing, column 1 is a conventional fractional distillation column, e.g. one of the bubble cap type containing, for example, 25 bubble plates. To simplify the description, equipment usually associated with such a column, e.g. pumps, valves and gauges, is not shown. Correct placement of such items will be apparent to any person skilled in the art.

The feed which enters the column through line 2 may be, for example, a cracked aromatic oil having the composition shown in Table 1 below, vaporized and heated to a temperature between 290 and 320 C. Feed enters the column at about the 20th plate from the top. If desired, additional xylene or mixtureof xylenes may be added to line 2 through :line .4 by opening valve 5. This additional material should be at .such a temperature that the resulting mixture is a vapor of the desired temper.- ature. The total concentration of xylenes in the feed entering the column is suitably in the range between 2 and percent by weight.

The stream to he used as liquid reflux is withdrawn through line .6, which is located at an intermediate-point in the column where the liquid composition and temperature are such that substantially no monomeric cyclopentadiene ispresent in the liquid and where no substan tial amountlof cyclopentadiene dimer or polymer has been formed. Line 6, for example, is arranged -to with draw liquid from: the 10th, 11th or 12th plate from the top, at atemperature of about 150 C. Thel'1qu1d-w1thdrawn through line 6 is cooled in cooler '8, e.g. to a term perature of 40 C., and is collected in accumulator 5 from which it is withdrawn through line 10. Some of this liquid may be withdrawn as side streamproduct by opening valve 12 in line 14. All, or the remainder of the liquid is returned as reflux 'to the top of the column via line 11. The vapor temperature at the top of the column is in-the range from-60 to 90 C. and the overhead vapors withdrawn through line 16 comprise monomeric cyclopentadiene and may contain some xylene. A side stream comprising unsaturated compounds suitable for the production of resins, specifically methyl styrenes and indene boiling in the range between 150 and 190 C. is withdrawn via line 15' which takes-liquid, for example, from the 16th plate from the top. The withdrawn liquid is-su'bstantially free of cyclopentadiene dimer and monomer and is suitable for the production of resins of good color and light stability. Liquid boiling higher than the side stream'is withdrawn as bottoms through line 12% and passes through reboiler 19. Part of this material is returned to the column through line 20 to supply heat for the distillation and part is withdrawn through line 21 for other uses.

The invention was carried into effect with a hydrocarbon mixture derived from a cracked petroleum fraction and having the approximate composition shown in Table 1.

Table 1 Component: Percent by weight Cyclopentadiene as monomem 3.4 Xylenes 4.9 150 C.1'90 C. fraction 26.6 190 C.230 C. fraction 25.3 Boiling above 230 C Remainder This was fed for a period of 10 days to a tube still where it was vaporized and the resulting vapors at a temperature of 300 C. were fed to the 20th plate from the top of a fractionating column having plates. Reflux withdrawn from plate 11.at 150 C. and cooled to 40 C., was returned to the top of the column. In this way, the1cyclopentadiene contained in the original mixture was ob tained substantially entirely in the overhead product. A side streamof boiling range-150190 C. from plate 16 was foundto be virtually free from cyclopentadiene.

During the operation of this distillation column the bromine number of the down-coming reflux stream. remained substantially constant between 40 and due principally to the presence of styrene in the crude xylene fraction. There was therefore no accumulation of cyclopentadiene in this stream. The overhead product was found to have abrornine number which did not vary beyond the range 120-,140throughout. the operationindicating a substantially constant cyclopentadiene content of about 35 percent by weight.

Resins formed from the methyl styrene and related compounds in the side stream had a greatly improved color and light stability compared with the case in which conventional reflux was employed under otherwise identical conditions.

I claim as my invention:

1. A process for the recovery of valuable organic compounds from a mixture consisting of cyclopentadiene and higher boiling compounds, including in substantial concentration at least one resin-forming unsaturated compound boiling between and 200 C., and xylene which comprises charging said mixture in vapor phase to the lower part of a fractional distillation column, adding as sole external reflux to said column, near the top thereof, a stream of Xylene, Withdrawing an overhead vapor stream consisting essentially of cyclopentadiene; withdrawing a first liquid side stream boiling mainly in the xylene boiling range comprising essentially said xylene and free of cyclopentadiene and polymers thereof, cooling said first side stream and returning at least part thereof as said external reflux; withdrawing at least a second liquid side stream boiling between 150 and 200 0, comprising at least one of said unsaturated resin-forming compounds and essentially free of cyclopentadiene and polymers thereof, and recovering resin-forming unsaturated compounds as products from said side stream.

2. A process for the recovery of valuable organic compounds from a mixture consisting of cyclopentadiene, xylene and higher boiling compounds, including in substantial concentration at least one resin-forming compound selected from the group consisting of methyl styrene isomers and indene, which comprises charging said mixture in vapor phase at a temperature between 290 and 320 C. to the lower part of a fractional distillation column, adding as sole external reflux to said column, near the top thereof, a xylene stream cooled to a temperature of about 40 C. and obtained from a source described hereinafter, withdrawing a cyclopentadiene overhead vapor stream and recovering purified cyclopentadiene from said overhead stream; withdrawing from an intermediate point of the column, where the liquid composition and temperature is such that; substantially no monomeric cyclopentadiene can be present in solution and where there has been no formation of any substantial amount of dimeric cyclopentadiene, a first liquid side stream boiling mainly in the xylene boiling range, comprising xylene and free of cyclopentadiene and polymers thereof, cooling said first side stream and returning at least a part thereof as said external reflux; withdrawing at least a second liquid side stream boiling between 150 and 200 C., comprising at least one of said resin-forming compounds and essentially free of cyclopentadiene and polymers thereof, and recovering said resin-forming compounds as product from said side stream.

3. A process according to claim 2 in which the concentration of cyclopentadiene in said mixture is in the range from 1 to 10 percent by weight, that of the xylene in the range from2 to 10 percent by weight, and that of said resin-forming compounds from 15 to SOpercent by weight.

References Cited in the file of this patent Wilson et al.: The Chemistry and Utilizationof Cyclopentadiene (Baltimore, 1944). Reprinted from-Chemical Reviews, .vol. 34-, #1, February 1944. Copy in Div. 31.) 

1. A PROCESS FOR THE RECOVERY OF VALUABLE ORGANIC COMPOUNDS FROM A MIXTURE CONSISTING OF CYCLOPENTADIENE AND HIGHER BOILING COMPOUNDS, INCLUDING IN SUBSTANTIAL CONCENTRATION AT LEAST ONE RESIN-FORMING UNSATURATED COMPOUND BOILING BETWEEN 150* AND 200*C., AND XYLENE WHICH COMPRISES CHARGING SAID MIXTURE IN VAPOR PHASE TO THE LOWER PART OF A FRACTIONAL DISTILLATION COLUMN, ADDING AS SOLE EXTERNAL REFLUX TO SAID COLUMN, NEAR THE TOP THEREOF, A STREAM OF XYLENE, WITHDRAWING AN OVERHEAD VAPOR STREAM CONSISTING ESSENTIALLY OF CYCLOPENTADIENE; WITHDRAWING A FIRST LIQUID SIDE STREAM BOILING MAINLY IN THE XYLENE BOILING RANGE COMPRISING ESSENTIALLY SAID XYLENE AND FREE OF CYCLOPENTADIENE AND PLYMERS THEREOF, COOLING SAID SIDE STREAM AND RETURNING AT LEAST PART THEREOF AS SAID EXTERNAL REFLUX; WITHDRAWING AT LEAST A SECOND LIQUID SIDE STREAM BOILING BETWEEN 150* AND 200*C., COMPRISING AT LEAST ONE OF SAID UNSATURATED RESIN-FORMING COMPOUNDS AND ESSENTIALLY FREE OF CYCLOPENTADIENE AND POLYMERS THEREOF, AND RECOVERING RESIN-FORMING UNSATURATED COMPOUNDS AS PRODUCTS FROM SAID SIDE STREAM. 